Calibration and Data Reporting Formats
For particle counter calibration, ISO 11171 refers to the NIST traceable procedure whereas ISO 4402 refers to the old ACFTD method. For example, ISO 11171 particle size data is expressed as “X pro(c)”, where ISO 4402 data was presented as “x pm” (x = particle size). What’s important to note is particle sizes acquired with ISO 11171 calibration are not the same as those obtained with ISO 4402.
The ISO technical committee adopted a revised procedure for reporting fluid-cleanliness measurements calibrated with the NIST-traceable method. ISO 4406:1999 uses three-code numbers corresponding to concentrations of particles larger than 4 µm(c), 6 µm(c)and 14 µm(c). The 1999 sizes matched up closely with the ISO4406 coding-system sizes (5 µm & 15 µm), once measured with ACFTD calibrated particle counters. However, the 4 µm(c) measurement equates to ~1 µm size if the ACFTD calibration procedure had been used.
Fluid cleanliness is now characterized from 0.01 - 2,500,000 particles/mL in three bin ranges with a series of numerical codes to indicate the count in each bin:
Particle Size Measurements
ACFTD Sizes (µm) ISO 4402: 1991 |
NIST-Calibrated Sizes µm(c) ISO 11171 |
<1.0 |
4.0 |
1.0 |
4.2 |
2.0 |
4.6 |
2.7 |
5.1 |
3.0 |
5.1 |
4.3 |
6.0 |
5.0 |
6.4 |
7.0 |
7.7 |
10.0 |
9.8 |
12.0 |
11.3 |
15.0 |
13.6 |
15.5 |
14.0 |
20.0 |
17.5 |
25.0 |
21.2 |
30.0 |
24.9 |
40.0 |
31.7 |
50.0 |
38.2 |
100.0 |
70.0 |
Fluid cleanliness is now characterized from 0.01 - 2,500,000 particles/mL in three bin ranges with a series of numerical codes to indicate the count in each bin:
- First code indicates particle count above 4 microns
- Second code indicates particle count above 6 microns
- Third code indicates particle count above 14 microns